1. Field of the Invention
The present invention relates to a golf ball where the high durability is required for the mark and the coating film like golf balls used in a golf practice shooting range, more particularly, to a golf ball which exhibits the superior adhesion of the coating film and the superior durability of the mark even if the golf ball is repeatedly subjected to shot and cleaning.
2. Description of the Related Art
A golf ball is coated with a clear coating film free of any pigment, or a coating film containing pigment. The coating film can impart the gloss to the golf ball surface, thereby improving the appearance and protecting the printed mark and number. In recent years, there is a tendency to prefer a golf ball having an ionomer resin cover finished with a clear paint, because such a golf ball is excellent in gloss and color tone. Generally, a polyurethane clear coating film is applied as the clear coating film covering the golf ball surface, because the polyurethane clear coating film has superior stretch ability and hence is easy to follow the deformation of the golf ball when it is shot.
However, the polyurethane clear coating film tends to peel off, because the adhesion between the polyurethane clear coating film and the ionomer cover is not sufficient. Further, the sunlight passes through the polyurethane clear coating film and acts directly upon the ionomer cover, thereby lowering the adhesion between the ionomer cover and the polyurethane clear coating film, when the golf ball covered with the polyurethane clear coating film is exposed to the outside.
In view of this problem, when the clear coating film is formed as a surface layer of the golf ball having the ionomer resin cover, it is proposed that a primer coat having adhesion to both the ionomer resin cover and the polyurethane clear coating film is applied between the cover and the clear coating film.
For example, Japanese Unexamined Patent Publication No. H08-182775 has proposed a primer layer which is made from the polyurethane paint. The polyurethane paint is obtained by mixing a polyol and polyisocyanate so that the amount of hydroxyl group of the polyol becomes in excess relative to the amount of isocyanate group of the polyisocyanate in molar ratio. The above polyurethane paint has superior adhesion to the ionomer cover and ensures the sufficient adhesion between the primer layer and the clear topcoat if the polyurethane clear coat with the similar composition is used.
Japanese Unexamined Patent Publication No. S61-119283 has proposed a golf ball having an ionomer resin cover onto which an epoxy clear coating film having a good adhesion thereto is formed as a primer film, and then the polyurethane clear coating film is formed on the primer film. In addition, the ultraviolet light resistance of the ionomer resin cover is improved by adding barium sulfate, a blue colorant, or a fluorescent brightener or the like thereinto.
The golf boll used in the golf practice shooting range is hit many times, used repeatedly after cleaning, and exposed to the outside much more times than the golf ball for personal use. In this case, the peel-resistance and the cleaning-resistance are highly required for the clear coating film and the mark of the golf ball. In view of this point, the conventional combination of the primer layer and the clear coating film does not meet with this requirement sufficiently, and the higher durability is required for the golf ball.
The present invention has been achieved in view of the above problems. Accordingly, it is an object of the present invention to provide a golf ball with the highly enhanced durability of the clear coating film and the mark.
The inventor of the present invention has found that: an epoxy coating film prepared by curing an epoxy resin with a polyamide curing agent has superior compatibility with and adhesion to both of the ionomer resin cover and the polyurethane clear coating film; and the use of a specific polyol imparts a superior durability against the deformation when hit and against alkali cleaning to the polyurethane clear coating film, and has achieved the present invention.
According to the present invention, there is provided a golf ball comprising: a ball body having an ionomer resin cover; an epoxy coating film formed on the ball body, and a polyurethane clear coating film formed on the epoxy coating film, wherein the epoxy coating film is made by curing an epoxy resin with a polyamide curing agent; and the polyurethane clear coating film is made by curing a polyol with an isocyanate curing agent, wherein the polyol is a mixture of a polyester polyol and a polyether polyol.
The foregoing and other objects, features and attendant advantages of the present invention will become apparent from the reading of the following detailed description in conjunction with the accompanying drawing.